Communication satellite payloads typically use high power amplifiers to increase power of received signals. The high power amplifiers are grouped together in redundancy rings, such that each high power amplifier within the ring has the same operating frequency range, bandwidth, and output power. For example, a commercial satellite may include 40 Ku-Band 120 W traveling wave tube amplifiers, 24 C-Band 40 W traveling wave tube amplifiers, and 38 90 W Ka-Band traveling wave tube amplifiers. Each high power amplifier is required to meet down link power or effective isotropic radiated power (EIRP) requirements equivalent to adjacent high power amplifiers contained within a redundancy ring. However, different paths through the redundancy ring have varying amounts of loss and not all of the high power amplifiers have identical EIRP requirements. Therefore, extra power is provided to high power amplifiers that have lower EIRP requirements. This is generally not power efficient.
Additionally, current high power amplifiers are limited in that they are designed and manufactured for one specific performance application. A performance application may be associated with providing service to a specific service area or serving or providing backup to a particular business service plan. Differing performance applications require different output RF power levels.
In conventional satellite payloads a high power amplifier typically includes a power supply that monitors cathode current of a high power amplifier and adjusts anode voltage to maintain a constant cathode current via an analog feedback loop. Over time, as a cathode of the high power amplifier degrades, the power supply compensates for this change by adjusting anode voltage to maintain a constant cathode current for a single designed performance application.
Current power systems for satellites determine minimum EIRP for high power amplifiers and adjust saturated power output of the high power amplifiers to the minimum EIRP, thereby reducing power consumption of the systems. Reducing the amount of power consumed by various components is desired because it not only conserves energy but also allows additional transponders to be placed upon a satellite to generate additional revenue.
Unfortunately, although the above stated systems provide high power amplifiers with variable output power that may be externally adjusted when in orbit; they do not provide a technique for maintaining constant overall power efficiency when operating with non constant amplitude (envelope) signals such as those present when multiple carriers are being amplified by the same amplifier.
It would therefore be desirable to provide a high power amplifier system that has reduced operating power consumption and that is capable of maintaining an approximately constant power efficiency regardless of the variability in the amplitude or envelope of the signals being amplified.